The primary objective of these studies is to determine if there are receptors for androgens in the central nervous system and to determine how other steroids affect the binding of androgens to these receptors. A secondary objective is to determine whether there are differences in binding between sexually "differentiated and undifferentiated" brains and between "differentiated male and female" brains. In order to accomplish these objectives, two principal approaches will be used. The first approach, autoradiography, will be used to determine the precise anatomical distribution of those neurons which concentrate testosterone and its unaromatized metabolites and of those neurons which aromatize testosterone to estradiol-17 beta before nuclear uptake and retention occurs. In addition, the ability of different nonradioactive steroids to modulate the binding of H3-steroids to these two populations of neurons will be investigated using autoradiography. The second approach to be used will be cell-free binding studies, to demonstrate the presence and biochemical properties of androgen receptors in both cytoplasm and nuclei of defined brain regions, and to identify the molecular basis of the nuclear retention already demonstrated by autoradiography.